The present invention relates to an electromagnetic interference repressor for preventing unwanted electronic waves from leaking out of electronic equipments, or for providing interferences between internal circuits and influences of miss-operation caused by external electronic waves. In practically, the present invention relates to electromagnetic interference repressor formed by composite magnetizer consisting of organic binder having soft magnetic powder dispersed therein.
Recently, an importance of a measure devised to deal with electromagnetic environmental problems in electronic equipments is recognized increasingly. This is supported by a background in which many kinds of electronic equipments provide circuits with higher densification than before and both active and passive elements each consisting of a semiconductor device, and the like, which radiate dielectric noise are congested increasingly. These are because electronic devices such as digital electronic equipments and the like aim at responding to requirements of accelerating circuit signal processing speed, higher frequency, higher performances of multifunction, down sizing and lower profiling of product configuration, in the back ground.
As a result, it is often caused to occur that normal operation of equipments are disturbed. This is caused by increase of line-to-line coupling due to electrostatic coupling and electromagnetic coupling and also by interference of radiation noise. In some cases, the noise may affect other external equipments.
As countermeasures against noise caused by electronic devices with higher processing speed, more advanced function and higher density, particularly, a countermeasure against noise caused in quasi-microwave band, installation of low pass filter, shielding and the like can be taken. However, a countermeasure by components requires space for installation in the electronic device and needs to consider down sizing and low profiling in design phase. The counter measure by components is therefore not suitable for an urgent measure. In addition an inductance component contributes to real number portion magnetic permeability xcexcxe2x80x2 and is insufficient for inductance in current quasi-microwave band. Further, in the event of conducting an inadvertent shielding, secondary electromagnetic coupling may be induced.
In response to the problems, the above-mentioned composite magnetizer sheet for repressing electromagnetic interference has been proposed as one of countermeasures against noise in quasi-microwave band. For example, proposals are made about composite magnetizer sheets capable of repressing electromagnetic interference in unexamined Japanese Patent Publication No. Hei 7-212079 and unexamined Japanese Patent Publication No. Hei 7-183911.
The above-mentioned composite magnetizer sheets correspond to quasi-microwave band and are capable of reducing permeability of radiation noise and secondary electromagnetic coupling as wave absorbers using high real number portion magnetic permeability xcexcxe2x80x2 and imaginary number portion magnetic permeability xcexcxe2x80x3 with a wide spectrum. Accordingly, it is possible to lighten the burden of the anti-noise measure and product development and to avoid impediments to achieve down sizing and higher densification of a circuit.
Further, in the market, a component of an anti-noise measure which is easy to use similar to the above-mentioned composite magnetizer and is capable of corresponding to retrofit components is required. The component of an anti-noise measure is preferred to have frequency band capable of component correspondence, that is, low frequency between about 10 to about 100 MHz in quasi-microwave band. Further, in the circumstance that down sizing of the electronic equipments is proceeding, the composite magnetizer sheet is required to have lower profiling corresponding to the above-mentioned quasi-microwave band.
The above-mentioned composite magnetizer sheet utilized for quasi-microwave band can provide less magnetic permeable ratio as the frequency becomes lower. Accordingly, providing lower profiling in configuration is limited and effect of repressing the electromagnetic interference reduces, as it is understood from the rise frequency of xcexcxe2x80x3. As another anti-noise measure which may be taken in small electronic equipments such as a mobile communications equipment, and the like, installing ferrite or rubber ferrite may be acceptable in idea. However, in most events, ferrite can not be installed because of the problems of a possibility to be cracked or a difficulty of placement. On the other hand, rubber ferrite which has less possibility to be cracked can not repress noise sufficiently, even though a space for installation is reserved.
Components such as coils, filters, and the like are usable in the frequency of a lower side and a higher side than the spectrum between about 10 to about 100 MHz. However, currently, no anti-noise measure which is easy to be used in the above-mentioned frequency band is found. Even if a component corresponding to such an anti-noise measure is found, change of design of a substrate, and the like requires a great deal of costs and man-hour.
To solve these problems, it becomes necessary to provide a composite magnetizer sheet adoptable to the spectrum of lower frequency between about 10 to about 100 MHz and capable of expressing the electromagnetic interference repressing effect even in the lower profiling thereof.
In order to provide such a composite magnetizer sheet, it becomes indispensable to enhance magnetic permeability xcexcxe2x80x2 and xcexcxe2x80x3 and depress magnetic resonance frequency. In response to these requirements, for example, a proposal is made about a composite magnetizer sheet in which the repressing effect in FM band between about 10 to about 100 MHz is improved and which is adjusted to lower profiling in unexamined Japanese Patent Publication No. Hei 10-168273. Improvements of the electromagnetic interference repressing effect and lower profiling in configuration has been achieved by using the technologies disclosed in the above-mentioned unexamined Japanese Patent Publication.
Here, description is made about an example of methods for forming the above-mentioned composite magnetizer. As methods for forming the above-mentioned quasi-microwave band composite magnetizer sheet, there are a wet process in which a blended and agitated slurry regime admixture of flat soft magnetic powder, binder and solvent for dissolve the binder is formed in membrane by using doctor blade, and the like, and a dry process in which an admixture of flat soft magnetic powder and binder is kneaded by kneader, and the like, and is formed by roll, and the like.
Further, in the method for manufacturing a composite magnetizer disclosed in the above-mentioned unexamined Japanese Patent Publication No. Hei 10-168273, flat soft magnetic powder in which stress-strain is eliminated is formed in sheets by wet process in order not to cause a strain to the flat soft magnetic powder in the forming process and pressure is added on the sheet surfaces in vertical direction by press, thus high density is achieved. Accordingly, it is possible to enhance the electromagnetic interference repressing effect in FM band and to correspond to lower profiling.
Even though the effect of repressing noise with frequency between about 10 to about 100 MHz is enhanced and profiling of the configuration become lower by the method disclosed in unexamined Japanese Patent Publication No. Hei 10-168273, it is possible to obtain a composite magnetizer having electromagnetic interference repressing effect reserved therein. However the composite magnetizer obtained by the above-mentioned method provides flame resistance insufficiently.
In addition, magnetic permeable property can not be obtained sufficiently only by coating, and in the event the flat soft magnetic powder is pressed for increasing fill factor to reserve high magnetic permeability, the flat soft magnetic powder gets strain in the result and obtaining property required is difficult.
Further, the composite magnetizer sheet disclosed in unexamined Japanese Patent Publication No. Hei 10-168273 with the thickness of more than 0.3 mm is poor in flexibility and provides less mechanical strength as the thickness become smaller in coating process, thus handling in the post processing becomes difficult.
Further more, in the above-mentioned composite magnetizer, phenomenon of secular changes caused by moisture penetration inside, in concrete, depression of density is found and coating of binder on the surface is required to improve high temperature high humidity resistance, regardless of the thickness.
Moreover, according to the above-mentioned dry process, flat soft magnetic powder in which strain is removed is supplied with the strain again. It is thereby difficult to obtain desirable characteristics.
It is therefore an object of the present invention to provide a composite magnetizer (e.g., xe2x80x9ccomposite magnetic materialxe2x80x9d) for electromagnetic interference repressor (e.g., xe2x80x9csuppressorxe2x80x9d) and a method of manufacturing the composite magnetizer and electromagnetic interference repressing effect are reserved and in which flame resistance and mechanical strength are provided, sufficiently therein by filling the flat soft magnetic powder, in which strain is removed, with high density.
Other objects of the present invention will become clear as the description proceeds.
According to an aspect of the present invention, there is provided a method of manufacturing a composite magnetizer in which flat soft magnetic powder that strain is removed and a binder are blended and kneaded to obtain an admixture, the admixture being formed in a sheet by molding means selected from the group consisting of roll molding, injection molding, and extrusion molding, characterized in that the binder includes a vinyl chloride resin with glass-transition temperature of not lower than 50xc2x0 C.
The binder may be a mixture of chlorinated polyethylene and vinyl chloride resin with glass-transition temperature of not lower than 50xc2x0 C.
The contents of vinyl chloride monomer in the vinyl chloride resin is between about 75 to about 90 mol %.
The mixing ratio of the chlorinated polyethylene and the vinyl chloride resin is between about 4:1 to about 1:4 in weight.
The flat soft magnetic powder may be oriented and arrayed in-plane direction of the composite magnetizer sheet (e.g., xe2x80x9ccomposite magnetic sheetxe2x80x9d) and bulk density (e.g., xe2x80x9cpacked densityxe2x80x9d) of the flat soft magnetic powder may be enhanced by applying roll working to the composite magnetizer sheet using a device selected from the group consisting of a reduction roll device, a calendar roll device, and a pressing device.
The reduction roll device and the calendar roll device may be provided with a roll which is made of a material selected from the group consisting of a rubber with rubber strength (e.g., xe2x80x9crubber hardnessxe2x80x9d) of not smaller than 90, and a polymeric material.
A composite magnetizer or a composite magnetizer sheet may be manufactured by the method.
According to another aspect of the present invention, there is also provided a method of manufacturing a composite magnetizer in which flat soft magnetic powder that strain is removed and magnetic coating of slurry regime consisting of a binder dissolved in a solvent are formed in a sheet by coating means selected from the group consisting of die-coating, gravure coating, and reverse coating, characterized in that the binder includes a vinyl chloride resin with glass-transition temperature of not lower than 50xc2x0 C.
The binder may be a mixture of chlorinated polyethylene and vinyl chloride resin with glass-transition temperature of not lower than 50xc2x0 C.
The contents of vinyl chloride monomer in the vinyl chloride resin is between about 75 to about 90 mol %.
The mixing ratio of the chlorinated polyethylene and the vinyl chloride resin is between about 4:1 to about 1:4 in weight.
The flat soft magnetic powder may be oriented and arrayed in-plane direction of the composite magnetizer sheet and bulk density of the flat soft magnetic powder may be enhanced by applying roll working to the composite magnetizer sheet using a device selected from the group consisting of a reduction roll device, a calendar roll device, and a pressing device.
The reduction roll device and the calendar roll device may be provided with a roll which is made of a material selected from the group consisting of a rubber with rubber strength of not smaller than 90, and a polymeric material.
A composite magnetizer or a composite magnetizer sheet may be manufactured by the method.
The flat soft magnetic powder used in the present invention can be obtained in a flattened shape by applying mechanical grinding to spherical or indefinite shaped coarse powder. In the process of grinding, strain is generated in the flat soft magnetic powder to deteriorate characteristics of the powder. However, the above-mentioned strain can be removed by conducting anneal process. It is necessary to conduct the anneal process so as to obtain the flat soft magnetic powder having desired characteristics. The conditions of the anneal process are determined, dependent on the materials of the soft magnetic powder as appropriate.
As mentioned above, there are dry process and wet process for forming the admixture of flat soft magnetic powder and binder in a sheet. The wet process is more preferable for reducing the load of external force onto the flat soft magnetic powder. In the present invention, composite magnetizer in which a flat direction of soft magnetic powder is oriented to in-plane direction of a sheet can be obtained by forming a membrane by die-coating, gravure coating or reverse coating.
In the present invention, vinyl chloride resin with glass-transition temperature of 50xc2x0 C. or more is used as a binder. Therefore, strength of binder at room temperature is increased. It becomes easier to handle the composite magnetizer in the work process.
The contents of chlorine in the binder are increased by using vinyl chloride resin. Thereby, flame resistance is enhanced. Further, high temperature and high humidity resistance of the composite magnetizer can be improved, since polyvinyl chloride has lower water vapor permeability than polyethylene.
In the present invention, the most preferable value of content of vinyl chloride monomer in the vinyl chloride resin for expressing the above-mentioned effect sufficiently is between about 75 to about 90 mol % and mixing ratio of chlorinated polyethylene and vinyl chloride resin is between about 4:1 to about 1:4 in weight.
It is effective to enhance the density of the composite magnetizer for obtaining the composite magnetizer with high magnetic permeability. High density can be implemented by applying roll working on the sheet after forming in membrane and removing the solvent. Therefore, in the method of manufacturing the composite magnetizer sheet of the present invention, a surface of the composite magnetizer sheet is pressed vertically by rolling device utilizing press or roll. The pressing brings a has secondary effect to enhance orientation extent of the flat soft magnetic powder.
During the above-mentioned process, if the press work is applied to the composite magnetizer inadvertently, strain is again generated in the flat soft magnetic powder. Therefore, a rolling device providing a roll consisting of rubber with rubber strength of not less than 90 or consisting of polymeric material is used in the present invention.